Fans are frequently used, for example, to push, pull, or circulate air through housings containing electronic equipment for cooling the electronic equipment. In some applications, controllers control these fans. For example, controllers can control fan speed, shut down malfunctioning fans, issue alarms when fans malfunction, etc. Many fan controllers place fans in a fault mode in the case of a fan fault, such as when fans are accidentally stopped, e.g., by an obstruction. In one application, a fault mode consists of issuing an alarm and no longer supplying power to the fan when a fan fault occurs. Problems occur, however, in cases of temporary fan faults, e.g., when a fan is temporarily obstructed and the obstruction is subsequently removed, thereby removing the fault. This is because many controllers require human intervention to restart the fan when the temporary obstruction is removed.
In some applications, fan controllers shut down fans at temperatures that can cause fan lubricants to freeze. This is often referred to as thermal shut down. However, while in a thermal shutdown mode, many controllers indicate that all fans are operable even though one or more of the fans became inoperable, e.g., due to an obstruction, prior to thermal shut down. Similar problems can occur when fans are manually shut down.
For the reasons stated above, and for other reasons stated below that will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for alternatives for controlling fans.